In a study posted to the medRxiv* preprint server, an interdisciplinary team of researchers from Europe analyzed the alterations of sphingolipids and their metabolizing enzymes in hospitalized or convalescent coronavirus disease 2019 (COVID-19) patients.
Study: COVID-19 and its clinical severity are associated with alterations of plasma sphingolipids and enzyme activities of sphingomyelinase and ceramidase. Image Credit: alessandro guerriero/Shutterstock
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection activates the acid sphingomyelinases (ASM)/Cer (cerine) system leading to the formation of Cer-enriched membrane domain and clustering of the cellular receptor for SARS-CoV-2, the angiotensin-converting enzyme 2 (ACE2) receptor, facilitating viral entry, infection, and consequent release of pro-inflammatory cytokines.
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
Many commonly used selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, fluvoxamine, amitriptyline functionally inhibit ASM and are called functional inhibitors of ASM (FIASMAs).
About the study
The researchers analyzed COVID-19 patient data of 125 men and 74 women hospitalized with mild, moderate, and severe symptoms in the current study. Blood samples were collected to estimate enzyme activity using fluorescent substrates - BODIPY-FL-C12 - sphingomyelin for ASM and neutral sphingomyelinases (NSM) and NBD-C12-ceramide for neutral ceramidase (NC).
The quantification of sphingolipids was performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Antibodies levels against SARS-CoV-2 in plasma donors were determined by two enzymes immunoassays - LIAISON® SARS-CoV-2 S1/S2 immunoglobulin G (IgG) semi-quantitative chemiluminescent immunoassay and SARS-CoV-2- enzyme-linked immunoassay (ELIA).
Findings
Blood samples from 48 patients with mild symptoms (23 men; age: median 53), 50 patients with moderate symptoms (34 men; age: 67), and 50 patients with severe symptoms (33 men; age: 69) were analyzed and compared with 51 convalescent patients (35 men; age: 36). The researchers observed a significant age difference (p< 0.001) among groups. No significant difference in sex distribution between the groups was observed (p = 0.107).
The researchers observed a significant association of COVID-19 disease severity with the ASM and NSM levels using linear regression analysis with age and sex as cofactors. ASM and NSM activity was low, higher, and highest in convalescent patients, patients, and severely affected patients, respectively.
On the other hand, in COVID-19 patients, the activity of NC hydrolyzing Cer significantly decreased in a severity-dependent manner. Age (p < 0.005) but not sex (p > 0.1) was significantly associated with the sphingolipid parameters in all models. The researchers used multinomial regression analysis and observed that enzyme activities predicted the symptoms severity groups vs. the convalescent group. For NSM and NC, it was severe vs. mild, and for NSM, severe vs. moderate.
In the entire cohort studied, no difference in enzyme activities was observed depending on sex, and similar alterations were observed in patients of both sexes. In female patients, a strong increase in ASM and a decrease in NC activity were observed compared to male patients.
The study results showed decreased levels of total plasma sphingomyelin and sphingomyelin species, 20:0, 22:0, and 24:0, as well as of dihydrosphingomyelin 20:0, 22:0, and 24:0 in more severely affected COVID-19 patients. Accordingly, levels of Cers 16:0 and 18:0 as products of ASM and NSM increased with the highest increase noted in severely affected patients.
Moreover, dihydroceramide levels 16:0 and 18:0 were elevated in more severely affected COVID-19 patients. Only dihydroceramide and Cer with the specific fatty acid chain length 24:0 were decreased in patients with more severe infection symptoms. Other factors of nominal significance in the statistical model were also altered in the same manner, for instance, increased Cers (20:0, 22:0, 24:1) and decreased sphingomyelins (16:0) or dihydrosphingomyelins (16:0, total) in patients with more severe infection. Moreover, dihydrosphingosine, sphingosine-1-phosphate, and sphingosine were lower in more severely affected patients.
SARS-CoV-2 antibodies levels of recovered patients were highly age-dependent (rSpearman = 0.414, p = 0.003) and had no association with sphingolipid enzyme activities. In a linear regression model with age and sex as cofactors, enzymes or sphingolipid parameters were not associated with SARS-CoV-2 antibody levels (all p > 0.1).
Conclusion
The current study demonstrated the association of SARS-CoV-2 infection with dysregulation of sphingolipid homeostasis in a severity-dependent manner. SARS-CoV-2 increased enzyme activities of ASM and NSM, leading to the reduction of sphingomyelins, while the activity of NC was reduced, leading to the accumulation of ceramides.
SARS-CoV-2 antibody levels in convalescent patients were associated with age but none of the sphingolipid parameters. The study highlighted the role of the sphingolipid-metabolizing enzymes as a potential biomarker to predict and track COVID-19 disease progression and add to the current understanding of underlying mechanisms for developing therapeutic targets against SARS-CoV-2.
This research work supported the use of FIASMAs against the SARS-CoV-2- related infections as they reduce Cer levels. The study did not consider the SARS-CoV-2-variants, and hence the results may not apply to newly emerging variants, including Omicron.
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
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